The present invention relates to a method for drying a honeycomb formed article.
A honeycomb structure is widely used for a catalyst carrier, various filters, and the like. Recently, a honeycomb structure has been attracting attention as a diesel particulate filter (DPF) for trapping particulate matter discharged from a diesel engine.
A honeycomb structure generally employs ceramic as the main component. Such a honeycomb structure is manufactured by adding water and various kinds of additives such as a binder to a ceramic raw material to prepare kneaded clay in the first place and subjecting the kneaded clay to extrusion forming to manufacture a honeycomb-shaped formed article (honeycomb formed article). A honeycomb structure can be manufactured by drying and firing the honeycomb formed article.
The honeycomb formed article can be dried by a drying method using microwaves having an advantage of high drying speed and the like (microwave drying method), a dielectric drying method using high-frequency energy generated by applying current between electrodes provided on the upper and the lower sides of the honeycomb formed article, or hot air drying method where drying is performed by introducing hot air generated by a gas burner or the like, alone or in combination of them (see, e.g., JP-A-2002-283329, JP-A-2002-283330, and WO No. 2005/023503).
However, in the microwave drying method, there is a case having difficulty in drying the whole honeycomb formed article at uniform speed because drying in the upper and lower end portions and the outer peripheral portion is behind in comparison with the other portions of the honeycomb formed article in the drying process. Since the honeycomb formed article shrinks due to evaporation of water, when the drying speed is not uniform, a defect such as a deformation and breakage is easily caused. Further, in recent years, the partition walls (ribs) separating the cells have become thinner, and a honeycomb structure having thinner partition walls more easily causes a deformation or the like.
In the dielectric drying, depending on the material having high dielectric constant or dielectric loss or the size and the shape of the honeycomb formed article (work) to be dried, there is a case of causing a crack in the honeycomb formed article because electro magnetic waves used for the dielectric drying promote uneven drying of the honeycomb formed article.
Therefore, it can be considered to dry the honeycomb formed article by hot air drying instead of relying on the microwave drying and the dielectric drying. However, there is a problem of easily causing a crack to deteriorate the quality and the yield even in the hot air drying method.
In view of the aforementioned problem, the present invention aims to provide a method for drying a honeycomb formed article, the method being capable of drying a honeycomb formed article in a shorter period of time with inhibiting generation of a defect such as a deformation or breakage.